Thread-milling cutter



Sept. 19, 1939. v STONE 2,173,401

THREAD-MILLING .CUTTER} Filed Feb. 10, 1939 VI/ /0 2 /5 A 7 7 r Patented Sept. 19,1939

UNITED STATES PATENT OFFICE THREAD-MILLING CUTTER Application February 10, 1939, Serial No. 255,639

7 Claims.

This invention has to do generally with circular cutters, and is more particularly concerned with cutters for internally or externally milling two-step threads on tubular work such as well p1pe.

While not so limited in its application, the cutter may be utilized to mill two-step threaded joint parts, where there is to exist an annular radially extending shoulder at the junction of the steps, such as shown in Patent #2,006,520 issued jointly to Frederick Stone and myself July 2, 1935, on Casing joint.

It is the general object of the invention to provide a milling cutter whereby threads of this character may be milled expeditiously and accurately, it being realized that in spite of the relative massiveness of the work it is highly important in joints of this character that the threads be of extreme accuracy and yet, for economic reasons, that they be cut with minimum expenditure of time and labor.

It is also an object of the invention to provide cutters of this character which are capable of withstanding severe conditions of service to which they are exposed without losing their accuracy, but which, when finally worn, may be easily refinished or resharpened without destroying the accuracy and efiicacy of the tool.

Reference will be had to the accompanying 3D drawing, in which:

Fig. 1 is a fragmentary section through one wall of the pin end of a joint showing the type of external threads adapted to be cut by my improved thread milling cutter;

Fig. 2 is an elevation of the mill of my improved design and adapted to cut a thread of the type shown in Fig, 2;

Fig. 3 is an end elevation of Fig. 2;

Fig. 4 is a section on line 4-4 of Fig. 3;

Fig. 5 is a fragmentary section through the box end of a joint, adapted to mate with the pin end of Fig. 1, and showing the type of internal thread adapted to be cut by my improved mill; and

Fig. 6 is an elevation of the cutter embodying my invention and adapted to cut the type of internal threads shown in Fig. 5.

In Fig. 1 there is illustrated a fragmentary section through the pin end of a well pipe joint,

which pin includes a relativelylarge-diameter step l0 and a relatively small-diameter step i I, there being a substantially square-cut, annular shoulder 9 between the steps at their juncture. External threads l2 and I 3 are provided on steps I El and II, respectively, the threads being of equal lead stantially square.

and there preferably being a cylindric blank l5 and H5 at the free ends of steps l0 and Il, respectively, the diameter of each blank being equal to the root diameter of the corresponding thread, and shoulder 9 being defined between blank l5 6 on the larger step and blank 8 on the smaller step, the last named blank being of the same diameter as the apex diameter of threads l3.

The thread milling cutter shown in Figs. 2 to 4, inclusive, is adapted to cut the thread shown in 10 Fig. 1 by plunging the rotating cutter into the work and, while the work is rotated through 360, moving the cutter longitudinally through a distance equal to the lead of the thread, all as is well understood by those familiar with thread 15 milling.

The thread milling cutter shown in Figs. 2 to 4, may be considered as made up of a substantially cylindric sleeve or body member 2| having a relatively-large-diameter step 22 and an adjacent, g relatively small-diameter step 23, there being formed an annular shoulder 1, preferably squarecut, at the junction of the steps. Cut on large and small steps 22 and 23, respectively, are hobbing threads 24 and 25 which threads are of 2 5.

the same pitch and, preferably, though not necessarily, having the same cross-sectional characteristics. They are here shown as being sub- It will be understood that while I have, for convenience, called these for- 30 mations hobbing threads, actually they are, as

in usual thread hobs, alternate annular grooves and ridges having no spiral or lead.

Thread 25 starts at the free end 26 of small step 23 but stops short of shoulder 1, thus leaving 35 annular blank 2?. Thread 24 on larger step 22 starts at shoulder 1 but stops short of the opposite end 28 of the step, thus leaving an annular blank 29. It will be noted that thread 24 is of such depth that its root diameter is greater than the apex diameter of thread 25, thus leaving shoulder I with an uninterrupted radial extent.

The peripheral face of the cutter is fluted, preferably spirally, as at 30, the flutes extending 4.5 from end to end of the cutter and thus defining end-to-end spiral teeth 3!. The leading faces 32 of the teeth extend approximately radially of the cutter, though preferably they have a slight rake angle, while the teeth are preferably eccentrically so relieved as at 33.

While I have referred to the cutter as sub stantially cylindrical and have spoken of annular blanks and of the threads as being cut on the peripheral faces of the steps, it will be appreciated that this terminology is merely used as a convenience of approach, for, as a matter of fact, the threads 24 and 25 are on the eccentric faces of the teeth and the cutter, as a whole, and the steps and blanks thereof are not truly cylindrical. However, the meaning of the terminology will be made clear by referring to the drawing and the portions to which the reference numerals are applied.

When the cutter becomes Worn, it is merely necessary to grind back cutting faces 32 until the mill is again sharp, for, While the teeth are eccentrically relieved and therefore their over-all diameters will decrease as shoulders 32 are cut back, in this type of tool the over-all diameter of the cutter is not critical, within certain limits, as it will continue to mill properly irrespective of its diameter within those limits.

It will be seen that when the mill is applied to blank work having the characteristics shown in Fig. 1 prior to the milling of the threads, the threading may be accomplished by moving the tool into cutting engagement with the periphery of the work, preferably by a plunge cut, and while rotating both the Work and tool, moving the tool axially with respect to the Work a distance equal to a pitch of the hobbing thread, while the work is making one complete revolution. Under the conditions illustrated, such an operation will result in threads 24 and 25 of the cutter, forming threads I3 and I2, respectively, on the work, while cutter blanks 21 and 29 will cut annular blanks I5 and I6, respectively. It will be understood that when reference is made to the cutter blanks, it is to apply to those portions of the leading edges of the teeth which define those cutter blanks.

Preferably, the thread I3 is started by plunging the cutter into the work so that the first thread will be spaced to the right of shoulder 9, thus leaving on pin-step H the annular blank 8 adjacent that shoulder.

C'utter 40, adapted to mill the threads in the box end 4| of pipe 42 (Figs. 5 and 6), is of the same general formation as cutter 20, except that the cutter is proportionately reduced in all its diameters and is of the opposite hand. Its body portion 43 is solid, rather than tubular as in the case of cutter 20, and it is integral with a taper shank 44, there being annular relief 45 between the body portion and shank.

Since, with the exception that the threads on pipe 42 are internal threads and that the cutter is of opposite hand and of smaller diameter than cutter 20, all parts of the box threads and parts of cutter 40 are similar to corresponding parts of the pin threads and cutter 20, they will be given the same reference numerals, primed, as those given to corresponding parts in Figs. 1 to 4, inclusive, and the description applied to the external hob may therefore be applied to the internal hob without the need for repetitive subject matter.

While I have shown and. described a preferred embodiment of my invention, it'will be understood various changes in design, structure and arrangement may be made Without departing from the spirit and scope of the appended claims.

I claim:

1. A circular, thread-milling cutter embodying a substantially cylindrical body member having a series of angularly spaced flutes cut in its peripheral face to leave longitudinally extendirg cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis and being eccentrically relieved rearwardly of that face, each tooth having a pair of adjacent, longitudinally extending steps, an annular, substantially squarecut shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread.

2. A circular, thread-milling cutter embodying a substantially cylindrical body member having a series of angularly spaced, spiral flutes cut in its peripheral face to leave spirally extending cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis and being eccentrically relieved rearwardly of that face, each tooth having a pair of adjacent, longitudinally extending steps, an annular, substantially square-cut shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread.

3. A circular, thread-milling cutter embodying a substantially cylindrical body member having a series of angularly spaced flutes cut in its peripheral face to leave longitudinally extending cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis and being eccentrically relieved rearwardly of that face, each tooth having a pair of adjacent, longitudinally extending steps, an annular, substantially square-cut shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, said thread starting near said shoulder but stopping short of the opposite end of the larger step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread.

l. A circular, thread-milling cutter embodying a substantially cylindrical body member having ascries of angularly spaced flutes cut in its peripheral face to leave longitudinally extending cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis and being eccentrically relieved rearwardly of that face, each tooth having a pair of adjacent, longitudinally extending steps, an annular, substantially square-cut shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread, said second mentioned thread starting at the free end of the smaller step and stopping short of the shoulder.

5. A circular, thread-milling cutter embodying a substantially cylindrical body member having a series of angularly spaced flutes cut in its peripheral face to leave longitudinally extending cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis and being eccentrically relieved rearwardly of that face, each tooth having a pair of adjacent, longitudinally extending steps, an annular, substantially square-cut shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, said thread starting near said shoulder but stopping short of the opposite end of the larger step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread, said second mentioned thread starting at the free end of the smaller step and stopping short of the shoulder.

6. A circular, thread-milling cutter embodying a substantially cylindrical body member having a series of angularly spaced flutes cut in its peripheral face to leave longitudinally extending cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis, each tooth having a pair of adjacent, longitudinally extending steps, an annular, substantially square-cut shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread.

7. A circular, thread-milling cutter embodying a substantially cylindrical body member having a series of angularly spaced flutes cut in its peripheral face to leave longitudinally extending cutting teeth therebetween, each tooth having its leading face extending approximately radially with respect to the body member axis and being ecentrically relieved rearwardly of that face, each tooth having a pair of adjacent, longitudinally extending steps, an annular shoulder extending radially inward from the larger-diameter step to the smaller diameter step at the step-juncture, a hobbing thread cut in the peripheral face of the larger step and to a depth short of the projected peripheral face of the smaller step, and a hobbing thread cut in the peripheral face of the smaller step and of the same pitch as the first mentioned thread.

ALBERT L. STONE. 

